Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless communication devices, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, video gaming devices, video game consoles, cellular or satellite radio telephones, and the like. Digital video devices implement video compression techniques, such as MPEG-2, MPEG-4, or H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), to transmit and receive digital video more efficiently. Video compression techniques perform spatial and temporal prediction to reduce or remove redundancy inherent in video sequences.
In video coding, video compression often includes spatial prediction, motion estimation and motion compensation. Intra-coding relies on spatial prediction to reduce spatial redundancy between video blocks within a given video frame. Inter-coding relies on temporal prediction to reduce temporal redundancy between video blocks of successive video frames of a video sequence. For inter-coding, a video encoder performs motion estimation to track the movement of matching video blocks between two or more adjacent frames. Motion estimation generates motion vectors, which indicate the displacement of video blocks relative to corresponding prediction video blocks in one or more reference frames. Motion compensation uses the motion vectors to identify prediction video blocks from a reference frame. After motion compensation, a residual video block is formed by subtracting the prediction video block from the original video block to be coded. The video encoder usually applies transform, quantization and transform coefficient coding processes to further reduce the bit rate associated with communication of the residual block.
Some video coding makes use of scalable techniques. For example, scalable video coding (SVC) refers to video coding in which a base layer and one or more scalable enhancement layers are used. For SVC, a base layer typically carries video data with a base level of quality. One or more enhancement layers carry additional video data to support higher spatial, temporal and/or SNR levels. The base layer may be transmitted in a manner that is more reliable than the transmission of enhancement layers. SVC techniques may be used in a number of video coding environments, and may be particularly useful in wireless broadcast settings, e.g., television-like broadcasts to wireless handsets.
Spatial scalability is one type of SVC scheme in which enhancement layers add spatial resolution to frames of the base layer. In this case, a base layer may define a number of base layer video blocks of coded data, and the enhancement layer may define number of enhancement layer video blocks. The number of enhancement layer video blocks may be greater than the number base layer video blocks, thereby adding spatial resolution to frames of a video sequence. In SVC settings that support spatial scalability, inter-layer prediction may be used to reduce the amount of data needed to convey the enhancement layer. In inter-layer prediction, video blocks of the enhancement layer that fully overlap with video blocks of the base layer may be coded via predictive techniques that are similar to motion estimation and motion compensation. In particular, in inter-layer prediction, the enhancement layer information may be coded based on predictive video blocks of the base layer. In this way, inter-layer redundancy is exploited to yield data compression.